Passive positioning procedure and use of single burst asap ftm sessions

ABSTRACT

Techniques for estimating a position of an observing station are disclosed based on capturing, at the observing station, a first and a second FTM message exchanged between a first messaging station and a second messaging station. At the observing station, a first time of arrival of the first FTM message and a second time of arrival of the second FTM message may be determined. Based on contents of one or more FTM messages, a first transmission-related time associated with the first FTM message and a second transmission-related time associated with the second FTM message may be obtained. The position of the observing station may be estimated based on (1) a position of the first messaging station, (2) a position of the second messaging station, (3) the first time of arrival, (4) the second time of arrival, (5) the first transmission-related time, and (6) the second transmission-related time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of U.S. Provisional PatentApplication No. 62/381,524, filed Aug. 30, 2016, and entitled “PASSIVEPOSITIONING PROCEDURE AND USE OF SINGLE BURST ASAP FTM SESSIONS,” whichis incorporated by reference herein in its entirety for all purposes.

BACKGROUND

Position determination is a key enabling feature that supports myriadsof applications and functions in modern devices. A mobile device, suchas a smart phone, that is capable of determining its own positionbecomes a much more useful device in the context of mapping, navigation,social applications, gaming, Internet of Things, and many other areas.Traditionally, position determination for a particular device involvesthe use of signals actively transmitted from and received by the device,to measure distances to other devices nearby, e.g., by using round triptime (RTT), and calculate a position estimate for the device. However,there are significant disadvantages associated with the activetransmission and reception of such positioning signals. One disadvantageis the risk of compromised privacy. By participating in the activetransmission and/or reception of signals for purposes of positiondetermination, a device may reveal its existence and/or otherinformation to nearby devices. Another disadvantage is powerconsumption. Active transmission and reception of signals for positiondetermination is often performed in addition to routine transmission andreception of data signals and other device operations and can create anadditional drain on the precious battery reserves of the device. Yetanother disadvantage is the lack of scalability. If a large number ofmobile devices in an area all require position determination, the sheernumber of active positioning signal transmissions and receptions thatmay occur simultaneously may overwhelm systems and devices, such asaccess points (APs), responsible for handling such traffic. There is apressing need for position determination techniques that can addressthese and other challenges.

SUMMARY

Embodiments of the disclosure relate to a technique for estimating aposition of an observing station. The technique may involve, at theobserving station, capturing a plurality of packetized FTM messagesexchanged between a pair of messaging stations comprising a firstmessaging station and a second messaging station. The plurality ofpacketized FTM messages may include a first FTM message originating fromthe first messaging station and intended for the second messagingstation and further include a second FTM message originating from thesecond messaging station and intended for the first messaging station.The technique may further involve, at the observing station, determininga first time of arrival corresponding to a time at which the first FTMmessage arrives at the observing station. According to at least oneembodiment, the first FTM message is part of an FTM session configuredfor an immediate, single burst (ASAP=1, burst exponent=0). The techniquemay further involve, at the observing station, determining a second timeof arrival corresponding to a time at which the second FTM messagearrives at the observing station. In addition, the technique may involveobtaining, based on contents of one of the plurality of packetized FTMmessages, a first transmission-related time associated with transmissionor reception of the first FTM message from the first messaging stationto the second messaging station. The technique may also involveobtaining, based on contents of one of the plurality of packetized FTMmessages, a second transmission-related time associated withtransmission or reception of the second FTM message from the secondmessaging station to the first messaging station. The position of theobserving station may be estimated based on (1) a position of the firstmessaging station, (2) a position of the second messaging station, (3)the first time of arrival, (4) the second time of arrival, (5) the firsttransmission-related time, and (6) the second transmission-related time.

The first FTM message may be an FTM frame, and the second FTM messagemay be an acknowledgement message acknowledging the FTM frame. The firsttransmission-related time may be a time of departure (ToD) correspondingto transmission of the first FTM message, as a first FTM frame, M, fromthe first messaging station. The second transmission-related time may bea time of arrival (ToA) corresponding to reception of the second FTMmessage, as an acknowledgement frame for the first FTM frame, M, at thefirst messaging station. The first transmission-related time and secondtransmission-related time may be obtained based on contents of asubsequent FTM frame, M+1.

The configuration of the FTM session as an immediate, single-burst FTMsession (ASAP=1, burst exponent=0) may be requested by one of the firstand second messaging stations and not subject to override by the otherof the first and second messaging stations. The FTM session may beinitiated by an FTM request message, and the configuration of the FTMsession as an immediate, single-burst FTM session (ASAP=1, burstexponent=0) may be indicated by a bit in a trigger field in the FTMrequest message. According to an embodiment, at least one of thecaptured packetized FTM messages utilizes a modified FTM frame format.The modified FTM frame format may replace a plurality of informationelement (IE) parameter fields with a plurality of new fields. Theplurality of new fields may include one or more of a Max Burst Durationfield, a Min Delta FTM field, a Max FTMs per burst field, a FTM Formatand Bandwidth field, a Status field, or a reserved field.

In one embodiment, estimating the position of the observing stationinvolves determining a differential distance corresponding to adifference between (a) a distance between the first messaging stationand the observing station and (b) a distance between the secondmessaging station and the observing station. The differential distancemay be determined based on (1) the first time of arrival, (2) the secondtime of arrival, (3) the first transmission-related time, and (4) thesecond transmission-related time. The position of the observing stationmay be determined based on the differential distance, the position ofthe first messaging station, and the position of the second messagingstation.

According to one embodiment, technique for estimating the position ofthe observing station may further involve obtaining the position of thefirst messaging station and the position of the second messaging bydownloading, from a server, a portion of an almanac comprising a list ofmessaging stations and corresponding locations. The technique may alsoinvolve capturing a plurality of packetized FTM messages exchangedbetween a second pair of messaging stations. Estimating the position ofthe observing station may be further based on positions of the secondpair of messaging stations, times of arrival, at the observing station,of a first and a second FTM message associated with the second pair ofmessaging stations, and first and second transmission-related timescorresponding to the first and second FTM messages associated with thesecond pair of messaging stations.

Certain embodiments of the disclosure relate to an apparatus forestimating a position of an observing station. The apparatus maycomprise a wireless communication interface configured to capture aplurality of packetized FTM messages exchanged between a pair ofmessaging stations comprising a first messaging station and a secondmessaging station. The plurality of packetized FTM messages may includea first FTM message originating from the first messaging station andintended for the second messaging station and further include a secondFTM message originating from the second messaging station and intendedfor the first messaging station. The apparatus may further comprise aprocessing unit coupled to the wireless communication interface, theprocessing unit configured to determine, at the observing station, afirst time of arrival corresponding to a time at which the first FTMmessage arrives at the observing station. According to at least oneembodiment, the first FTM message is part of an FTM session configuredfor an immediate, single burst (ASAP=1, burst exponent=0). Theprocessing unit may be further configured to determine, at the observingstation, a second time of arrival corresponding to a time at which thesecond FTM message arrives at the observing station. Also, theprocessing unit may be configured to obtain, based on contents of one ofthe plurality of packetized FTM messages, a first transmission-relatedtime associated with transmission or reception of the first FTM messagefrom the first messaging station to the second messaging station. Inaddition, the processing unit may be configured to obtain, based oncontents of one of the plurality of packetized FTM messages, a secondtransmission-related time associated with transmission or reception ofthe second FTM message from the second messaging station to the firstmessaging station. The processing unit may be further configured toestimate the position of the observing station based on (1) a positionof the first messaging station, (2) a position of the second messagingstation, (3) the first time of arrival, (4) the second time of arrival,(5) the first transmission-related time, and (6) the secondtransmission-related time.

Certain embodiments of the disclosure relate to a system for estimatinga position of an observing station. The system may comprise means for,at the observing station, capturing a plurality of packetized FTMmessages exchanged between a pair of messaging stations comprising afirst messaging station and a second messaging station. The plurality ofpacketized FTM messages may include a first FTM message originating fromthe first messaging station and intended for the second messagingstation and further include a second FTM message originating from thesecond messaging station and intended for the first messaging station.The system may further include means for, at the observing station,determining a first time of arrival corresponding to a time at which thefirst FTM message arrives at the observing station. In at least oneembodiment, the first FTM message is part of an FTM session configuredfor an immediate, single burst (ASAP=1, burst exponent=0). The systemmay further include means for, at the observing station, determining asecond time of arrival corresponding to a time at which the second FTMmessage arrives at the observing station. The system may further includemeans for obtaining, based on contents of one of the plurality ofpacketized FTM messages, a first transmission-related time associatedwith transmission or reception of the first FTM message from the firstmessaging station to the second messaging station. The system mayinclude means for obtaining, based on contents of one of the pluralityof packetized FTM messages, a second transmission-related timeassociated with transmission or reception of the second FTM message fromthe second messaging station to the first messaging station. The systemmay include means for estimating the position of the observing stationbased on (1) a position of the first messaging station, (2) a positionof the second messaging station, (3) the first time of arrival, (4) thesecond time of arrival, (5) the first transmission-related time, and (6)the second transmission-related time.

Certain embodiments of the disclosure relate to a non-transitorycomputer-readable storage medium comprising machine-readableinstructions stored thereon. When executed by one or more processors,the instructions may cause the one or more processors to perform varioussteps. The instructions may cause the one or more processors to, at anobserving station, facilitate capturing of a plurality of packetized FTMmessages exchanged between a pair of messaging stations comprising afirst messaging station and a second messaging station. The plurality ofpacketized FTM messages may include a first FTM message originating fromthe first messaging station and intended for the second messagingstation and further include a second FTM message originating from thesecond messaging station and intended for the first messaging station.The instructions may cause the one or more processors to, at theobserving station, determine a first time of arrival corresponding to atime at which the first FTM message arrives at the observing station. Inat least one embodiment, the first FTM message is part of an FTM sessionconfigured for an immediate, single burst (ASAP=1, burst exponent=0).The instructions may cause the one or more processors to, at theobserving station, determine a second time of arrival corresponding to atime at which the second FTM message arrives at the observing station.The instructions may cause the one or more processors to obtain, basedon contents of one of the plurality of packetized FTM messages, a firsttransmission-related time associated with transmission or reception ofthe first FTM message from the first messaging station to the secondmessaging station. The instructions may cause the one or more processorsto obtain, based on contents of one of the plurality of packetized FTMmessages, a second transmission-related time associated withtransmission or reception of the second FTM message from the secondmessaging station to the first messaging station. The instructions maycause the one or more processors to estimate the position of theobserving station based on (1) a position of the first messagingstation, (2) a position of the second messaging station, (3) the firsttime of arrival, (4) the second time of arrival, (5) the firsttransmission-related time, and (6) the second transmission-related time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram of a system that includes the basicentities involved in a passive position determination technique,according to embodiments of the present disclosure;

FIG. 2 is a signal diagram showing examples of Fine Timing Measurement(FTM) frames used in passive positioning, in accordance with certainembodiments of the disclosure;

FIG. 3 illustrates a modified FTM frame format that replaces certainfields and is suitable for a deterministic FTM session having animmediate, single burst of frames;

FIG. 4 illustrates new FTM parameters that can be adopted in the contextof a new frame format, in accordance with certain embodiments of thedisclosure;

FIG. 5A illustrates the placement of a new passive positioning FTMparameters element within a field in an FTM request message;

FIG. 5B illustrates the placement of the new passive positioning FTMparameters element within a field in an FTM frame;

FIG. 6 is a flow chart depicting a process for estimating a position ofan observing station, according to an embodiment of the disclosure;

FIG. 7 illustrates an embodiment of the observing station 106, as amobile device 700, which can be utilized as described herein above; and

FIG. 8 illustrates an embodiment of the messaging stations 102 and 104,as an access point (AP) 800, which can be utilized as described hereinabove.

DETAILED DESCRIPTION

Several illustrative embodiments will now be described with respect tothe accompanying drawings, which form a part hereof. While particularembodiments, in which one or more aspects of the disclosure may beimplemented, are described below, other embodiments may be used andvarious modifications may be made without departing from the scope ofthe disclosure or the spirit of the appended claims.

Passive Positioning

FIG. 1 is a simplified diagram of a system 100 that includes the basicentities involved in a passive position determination technique,according to embodiments of the present disclosure. System 100 is shownto include a first messaging station 102, a second messaging station104, and an observing station 106. Here, the term “station” broadlyrefers to a device that is capable of sending and/or receiving messagesvia a communication protocol with one or more other devices. A stationmay be stationary (e.g., base station) or movable (e.g., mobilestation). A station may have a designated role, depending on thecommunication protocol used. For example, in a wireless local areanetwork, one station may take on the role of an access point (AP), andanother station may take on the role of a client served by the AP. Asused in the present disclosure, a “messaging station” refers to astation that is involved in an exchange of messages with one or moreother stations. Generally speaking, the messages are composed of packetsof data. Each packet of data may have a certain structure, such as aframe structure, with multiple bit fields within each frame. As shown inthe figure, the first messaging station 102 and the second messagingstation 104 are involved in an exchange of messages with one another.Here, the exchange of messages includes a first packetized message 108transmitted from the first messaging station 102 to the second messagingstation 104. The first packetized message 108 is associated with a timeof departure (ToD) of t₁ from the first messaging station 102 and a timeof arrival (ToA) of t₂ at the second messaging station 104. The exchangeof messages also includes a second packetized message 110 transmittedfrom the second messaging station 104 to the first messaging station102. The second packetized message 110 is associated with a ToD of t₃from the second messaging station 104 and a ToA of t₄ at the firstmessaging station 102. According to various embodiments of thedisclosure, one or more of these times of arrival and/or departure maybe used in a passive positioning technique employed by an observingstation.

As shown in FIG. 1, the observing station 106 is not involved in theexchange of messages between the first messaging station 102 and thesecond messaging station 104. Instead, the observing station 106 ismerely “listening in” on the exchange of messages. For example, theobserving station 106 captures the first packetized message 108transmitted by messaging station 102 and intended for messaging station104. The observing station 106 also captures the second packetizedmessage 110 transmitted by messaging station 104 and intended formessaging station 102. In certain embodiments, messaging stationstransmit in a non-directional manner. Thus, any device within a certainrange may be able to capture a packetized message that is sent andintended for a particular targeted device. In other embodiments,messaging stations transmit in a directional manner. However, even inthat case, the directional transmission may still reach other devices inthe general direction or vicinity of the target device. Thus, innon-directional and even some directional transmission scenarios, anobserving station such as station 106 may be able to capture packetizedmessages exchanged between messaging stations such as stations 102 and104. As shown in FIG. 1, the first packetized message 108 reaches theobserving station at a ToA of t_(c1). The second packetized message 110reaches the observing station at a ToA of t_(c2). The observing station106 may record both t_(c1) and t_(c2) and utilize these values inperforming passive positioning.

According to embodiments of the disclosure, passive positioningtechniques employ the concept of “differential distance” in determiningthe position of the observing station 106. Here, the differentialdistance may represent the difference between (1) the distance betweenthe first messaging station 102 and the observing station 106 and (2)the distance between the second messaging station 104 and the observingstation 106. In the context of Fine Timing Measurement (FTM) messages,which will be explained in more detail below, a differential distancemay be expressed as follows:

D _(SR) =c×(T _(SO) −T _(RO))

where

-   -   c is the speed of light.    -   T_(SO) is the time of flight between the responding station        (STA) (e.g., first messaging station 102) and the observing        station (e.g., station 106)    -   T_(RO) is the time of flight between the initiating station        (STA) (e.g., second messaging station 104) and the observing        station (e.g., station 106)

The values T_(SO) and T_(RO) can be determined based on various times ofarrival (ToA) and times of departure (ToD) of relevant signals. Forexample, T_(SO) and T_(RO) may be determined as:

T _(SO) =t _(c1) −t ₁

T _(RO) =t _(c2) −t ₃ =t _(c2)−(t ₄ −T)

where T is the time of flight between the responding STA and theinitiating STA. The value of T may be found in various ways. Just as anexample, given the known positions of responding STA (e.g., firstmessaging station 102) and the initiating STA (e.g., second messagingstation 104), the distance T between the two messaging stations can bedetermined.

Thus, the differential distance can be expressed in terms of varioustimes of arrival and times of departure. For example:

D _(SR) =c×(t _(c1) −t _(c2) −T−(t ₁ −t ₄))

According to embodiments of the disclosure, the observing station 106may record the times of arrival t_(c1) and t_(c2) on its own. Theobserving station 106 may also extract certain times of arrival andtimes of departure, such as t₁ and t₄, from the contents of thepacketized messages exchanged between the messaging stations.

A differential distance, such as described above, serves as a basis fordetermining the position of the observing station 106. Given the knownpositions of a pair of messaging stations and the differential distancefrom the observing station to the pair of messaging stations, ahyperbolic curve can be determined that represents the possiblepositions of the observing station 106. The same technique can berepeated with another pair of messaging stations and the same observingstation 106, to yield a different hyperbolic curve representing possiblepositions of the observing station 106. The intersection of the twohyperbolic curves can be determined as the estimated position of theobserving station 106. The technique can be repeated using one or moreadditional pairs of messaging stations to yield additional hyperboliccurve(s). Determining the intersection of the multiple curves mayincrease the accuracy of the estimated position.

The positions of the pair of messaging stations 102 and 104 may beobtained by the observing station 106 by downloading, e.g., from aserver, a portion of an almanac comprising a list of messaging stationsand their corresponding positions. Such a server may be, for example, alocation server and/or an almanac server. Messaging stations 102 and 104may be cellular network base stations, access points (APs), and/or thelike, and the almanac maintained at one or more servers may containlocation information relating to the known positions of each messagingstation.

Fine Timing Measurement (FTM) Context

FIG. 2 is a signal diagram showing examples of Fine Timing Measurement(FTM) messages used in passive positioning, in accordance with certainembodiments of the disclosure. Traditionally, FTM messages are used toperform ranging between a pair of messaging stations, i.e., to find thedistance between the two messaging stations. An FTM session may beinitiated by an initiating STA, which sends an FTM request message (notshown) to a responding STA. In response, the responding STA may send anFTM frame, such as FTM_1 (M=1) shown in the figure, to the initiatingSTA. The FTM frame (M=1) is associated with a time of departure (ToD) oft₁ from the responding STA and a time of arrival (ToA) of t₂ at theinitiating STA. Thereafter, the initiating STA may send an FTMacknowledgment (ACK) message back to the responding STA. The ACK messageis associated with a ToD of t₃ from the initiating STA and a ToA of t₄at the responding STA. The basic exchange of an FTM frame followed by anACK message represents the basis of an FTM session.

An FTM session may comprise of more than one round of exchange of FTMframe and ACK message. Typically, an FTM session comprises one or morebursts of such exchanges. Just as an example, in FIG. 2, a particularburst is shown to include three rounds FTM and ACK exchanges. Theseexchanges involve FTM frame (M=1) and its corresponding ACK message, FTMframe (M=2) and its corresponding ACK message, and FTM frame (M=3) andits corresponding ACK message.

Transmission-related times ToD and ToA, such as t₁, t₂, t₃, and/or t₄,may be communicated as part of the contents of the various FTM framesand ACK messages. ToA and ToD values recorded for one FTM frame may becommunicated in a subsequent FTM frame. For example, timestamps t₁ andt₄ are determined at the Responding STA. The t₁ and t₄ values measuredfor a particular FTM frame, M, may be communicated in a subsequent FTMframe, M+1, from the Responding STA to the Initiating STA.

According to embodiments of the disclosure, passive positioning takesadvantage of the existing structure and functionality of FTM framesexchanged between an initiating STA and a responding STA. Themeasurement of transmission-related times, such as t1 and t4, and thecommunication of these values inside the contents of FTM framesrepresent functionality that already exists in FTM sessions. By merelylistening in on FTM exchanges and taking advantage of the existing FTMstructure and functionality, an observing STA may determine its ownposition without actively participating in any on-going FTM exchangesbetween initiating STA(s) and responding STA(s).

The relationship between the messaging stations, such as initiating STAand responding STA, and the observing STA may differ depending onimplementation. In one example, the relationship is that of accesspoints (APs) serving mobile devices as clients in a wireless local areanetwork (WLAN). Thus, the initiating STA may be one AP, and theresponding STA may be another AP, while the observing STA may be amobile device that is served by one or both of the APs. That is, themobile device may rely on the APs as the points of access to a largerdata network. In another example, the initiating STA and responding STAmay not take on the role of APs. Instead, the initiating STA andresponding STA may be dedicated only to the exchange of messages usedfor passive positioning and do not act as APs serving the role ofproviding mobile devices with access to a larger data network.

Passive positioning, such as that described above in the context of anFTM implementation, has significant advantages over traditionalpositioning techniques that require active transmission and reception ofpositioning signals. One advantage is privacy. The observing STA merelylistens in on exchanges of messages between messaging stations, withoutactively participating in such exchanges. Thus, the observing STA doesnot need to provide its identity or other information, which istypically required in establishing a message exchange. The initiatingSTA and responding STA may not even be aware of the existence of theobserving STA. Thus, the observing STA enjoys a high degree of privacywhen performing passive positioning. Another advantage is powerconsumption. Because the observing STA only needs to listen in onexisting message exchanges, the observing STA does not expend batteryresources in establishing message exchanges. The observing STA canrealize significant power savings over traditional positioningtechniques that require the active exchange, including transmission, ofpositioning signals. Yet another advantage is scalability. Passivepositioning can allow for virtually an unlimited number of observingSTAs to simultaneously perform positioning, by listening to theexchanges of messages among a limited number of messaging stations.Because the observing stations are merely listening, they do notrepresent an additional processing burden placed on the messagingstations. For example, if the mobile devices of 100,000 sports fans in astadium are simultaneously trying to obtain position information, all ofthe mobile devices may be able to perform passive positioning withoutscalability issues. In fact, a number of messaging stations can be setup (e.g., multiple pairs of messaging stations) to exchange messages,e.g., FTM frames, and all the mobile devices can perform passivepositioning by listening in on the exchanged messages without overtaxingthe capabilities of the messaging stations. Each additional mobilestation that listens in on the exchange of messages does not representan additional processing burden, from the perspective of the messagingdevices. Therefore, passive positioning is extremely well suited toscale up the number of observing stations.

Scheduled Passive Positioning

According to certain embodiments of the disclosure, it may beadvantageous to schedule the exchange of messages that are used by theobserving STA. As discussed, in certain scenarios, the initiating STAand responding STA may also serve as APs to provide network access tomobile devices. Specifically, the initiating STA may serve a group ofclients, e.g., mobile devices, by communicating with those clients on aparticular communication channel (e.g., a first frequency channel). Theresponding STA may serve another group of clients by communicating withthose clients on another communication channel (e.g., a second frequencychannel). In at least one implementation, an FTM session is establishedon a common communication channel. That is, the initiating STA and theresponding STA must agree to operate on a common communication channelover which the FTM frames are exchanged. For example, the initiating STAmay have to transition over to the communication channel currently usedby the responding STA, or vice versa. Such a transition may beburdensome on the clients of the STA (serving as the AP) that makes thetransition. That is, clients that were being served on a particularcommunication channel may no longer be able to find their AP on thatchannel--because the AP has transitioned to a different communicationchannel. Steps may need to be taken to warn, transition, or otherwiseassist the clients in dealing with such a transition.

To better handle such complications, messaging STAs that serve as APsmay exchange messages, such as FTM frames, based on a defined schedule.A defined schedule provides predictability and makes it possible for APsto transition to a new communication channel at defined time slots,thereby limiting the impact on their associated client devices. Adefined schedule also enables the observing STAs to align to theschedule when capturing the exchanged messages. For example, anobserving STA may “wake up” at the start of the appropriate time slot inorder to be able to timely receive one or more packetized messages(e.g., FTM frames and ACK messages) exchanged between messaging STAs.

Parameters of Negotiation

According to certain embodiments, messaging STAs may also negotiateparameters associated with the exchange of messages. Each STA, which mayserve as an AP to its own group of client devices, may have specificneeds and constraints. For example, one messaging STA may propose aparticular schedule for a message exchange, e.g., one or more FTMbursts. However, the proposed schedule may not be suitable or desirablefrom the perspective of the other messaging STA. Thus, by allowing themessaging STAs to negotiate parameters, it may be possible for themessaging STAs to agree on a particular set of parameters for theexchange of messages that is satisfactory to both entities. In variousembodiments, one or more of the following parameters may be negotiated.These parameters should be understood as being illustrative in natureand not exhaustive:

Length/duration of the passive positioning session

Response time

Spacing between each frame

Maximum number of successful frames to be exchanged in the session

Format of the frames (e.g., bandwidth, preamble, etc.)

Deterministic Passive Positioning Sessions

According to certain embodiments, a deterministic passive positioningsession is adopted, which can ease the process of scheduling and limitpower consumption at the observing STA. While there are advantages toallowing the messaging STAs to have flexibility in negotiating themanner in which the exchange of messages is to take place, too muchflexibility may lead to inefficient implementations. For example, theexisting structure of FTM frames allows for the option to delay themessage exchange, by controlling an “ASAP” parameter:

ASAP=1 (FTM burst starts immediately following FTM request message)

ASAP=0 (FTM burst is delayed and starts at time TSF)

In addition, as discussed previously, each FTM session may comprise oneor more bursts. Each burst may comprise one or more FTM frames (andcorresponding ACK messages). The number of bursts in an FTM session maybe controlled using a “burst exponent” parameter (n):

n=burst exponent

2^(n)=number of bursts in the FTM session

In some embodiments, an immediate, single burst of messages is chosen asa particularly useful configuration of a deterministic passivepositioning session. In the context of FTM frames, the ASAP parametermay be set to 1 (ASAP=1), and the burst exponent may be set to 0 (n=0).Using a single burst limits the impact on respective client devices ofeach messaging STA. A single burst is also sufficient for purposes ofexchanging enough messaging frames to be captured by the observing STAand used for passive positioning. Therefore, a single burst is asuitable choice for bounding the extent of the FTM session.

Furthermore, guidelines may be put in place to constrain the actions ofthe messaging STAs. For example, one guideline may dictate that, once aninitiating STA sends an FTM request message with ASAP=1 and burstexponent n=0, the responding STA is prohibited from overriding theASAP=1 and burst exponent n=0 parameters. In this example, theresponding STA may be constrained such that it is not allowed tooverride the immediate, single-burst nature of the proposed FTM session.However, the responding STA may still exercise some degree of control,because it can decide to either participate or not participate in theproposed FTM session. Thus, a balance is achieved, by providing adeterministic passive positioning session that is associated with easeof scheduling and relatively low power consumption.

Modifications to FTM Frame Format

FIG. 3 illustrates a modified FTM frame format that replaces certainfields and is suitable for a deterministic FTM session having animmediate, single burst of frames. To facilitate passive positioningthat achieves the previously discussed attributes of determinism,flexibility, and well-defined schedules, certain modifications may bemade to the currently existing FTM frame format. Some of thesemodifications are described below.

First, a bit in the FTM request message may be used to signal themandate to adhere to an immediate, single-burst FTM session. Forexample, the Trigger field in the FTM request message (e.g., as shown inFIG. 5A) has bits 0-7 reserved (i.e., values 0-255 reserved). One of thereserved bits can be used to indicate a request for an immediate, singleburst of FTM frames. That is, when set, the single bit may be used torepresent a request for setting the parameters ASAP=1 and burstexponent=0. When set, the same bit may also indicate that theconfiguration of ASAP=1 and burst exponent=0 is not to be overridden. Inother words, the initiating STA is proposing a specific type of FTMsession, and the responding STA is not free to modify the immediate,single-burst nature of the proposed FTM session.

Second, by adopting such a deterministic approach, certain fields withinthe existing FTM frame format may no longer be needed, because they wereoriginally intended as fields that specify certain parameters that arenow obsolete. For example, if it is “understood” that the FTM session isto have an immediate, single burst, i.e., ASAP=1, and burst exponent=0,it is no longer necessary for the FTM frame to include fields forexpressing values such as the number of burst exponents, partial TSFtimer (for indicating amount of delay before the FTM burst), ASAP, etc.

Referring to FIG. 3, the figure illustrates the existing fields of anFTM frame format, according to Section 9.4.2.168 of the 802.11REVmc D6.0standard. In particular, the frame format contains FTM informationelement (IE) parameters, which includes certain fields that becomeunnecessary and thus can be replaced:

Status Indication (B0-B1)

Value (B2-B6)

Reserved (B7)

Number of Burst Exponent (B8-B11)

Partial TSF Timer (B24-B39)

Partial TSF Timer No Preference (B40)

ASAP Capable (B41)

ASAP (B42)

Burst Period (B56-B71)

FIG. 4 illustrates new FTM parameters that can be adopted in the contextof a new frame format, in accordance with certain embodiments of thedisclosure. For passive positioning, a new FTM parameters element may beimplemented. The element may be referred to as “passive positioning FTMparameters element.” The new element may have an IE id. The IE id. ofthe new element may be specified using a reserved field from Table 9-77(e.g., 222-254) in the 802.11REVmc draft D6.0 standard.

FIG. 5A illustrates the placement of a new passive positioning FTMparameters element within a field in an FTM request message. As shown inthe figure, the new passive positioning FTM parameters element (“FineTiming Measurement Parameters”) may be placed in a variable length fieldwithin the frame format of the FTM request message.

FIG. 5B illustrates the placement of the new passive positioning FTMparameters element within a field in an FTM frame. As shown in thefigure, the same new passive positioning FTM parameters element (“FineTiming Measurement Parameters”) may be placed in a variable length fieldwithin the frame format of the FTM frame.

FIG. 6 is a flow chart depicting a process 600 for estimating a positionof an observing station, according to an embodiment of the disclosure.As shown, at step 602, the process involves, at the observing station,capturing a plurality of packetized FTM messages exchanged between apair of messaging stations comprising a first messaging station and asecond messaging station. The plurality of packetized FTM messages mayinclude a first FTM message originating from the first messaging stationand intended for the second messaging station and further include asecond FTM message originating from the second messaging station andintended for the first messaging station. Examples of the observingstation, first messaging station, and second messaging station may beobserving station 106, the first messaging station 102, and the secondmessaging station 104, respectively, as shown in FIG. 1. The first FTMmessage may be, for example, message 108 transmitted from the firstmessaging station to the second messaging station. The second FTMmessage may be, for example message 110 transmitted from the secondmessaging station to the first messaging station.

At step 604, at the observing station, the process involves determininga first time of arrival (e.g., t_(c1)) corresponding to a time at whichthe first FTM message arrives at the observing station, wherein thefirst FTM message is part of an FTM session configured for an immediate,single burst (ASAP=1, burst exponent=0). At step 606, at the observingstation, the process involves determining a second time of arrival(e.g., t_(c2)) corresponding to a time at which the second FTM messagearrives at the observing station. At step 608, the process involvesobtaining, based on contents of one of the plurality of packetized FTMmessages, a first transmission-related time (e.g., t₁) associated withtransmission or reception of the first FTM message from the firstmessaging station to the second messaging station. At step 610, theprocess involves obtaining, based on contents of one of the plurality ofpacketized FTM messages, a second transmission-related time (e.g., t₄)associated with transmission or reception of the second FTM message fromthe second messaging station to the first messaging station. At step612, the process involves estimating the position of the observingstation based on (1) a position of the first messaging station, (2) aposition of the second messaging station, (3) the first time of arrival(e.g., t_(c1)), (4) the second time of arrival (e.g., t_(c2)), (5) thefirst transmission-related time (e.g., t₁), and (6) the secondtransmission-related time (e.g., t₄).

According to certain embodiments, the steps depicted in process 600 mayall be performed at the observing station. For example, the observingstation may capture the first and second FTM messages and obtain, basedon contents of one of the plurality of packetized FTM messages in theFTM session, the transmission-related times associated with the firstand second FTM messages. The observing station may also estimate theposition of the observing station based on the known locations of thefirst and second messaging stations, the first and second times ofarrival, and the first and second transmission-related times. In otherembodiments, however, some of the steps depicted in process 600 may beperformed at the observing station, while other steps are performedelsewhere. For example, the observing station may capture the first andsecond FTM messages and obtain, based on contents of one of theplurality of packetized FTM messages, the transmission-related timesassociated with the first and second packetized messages. However,another entity, such as remote server, may estimate the position of theobserving station based on the known locations of the first and secondmessaging stations, the first and second times of arrival, and the firstand second transmission-related times.

FIG. 7 illustrates an embodiment of the observing station 106, as amobile device 700, which can be utilized as described herein above. Forexample, the mobile device 700 can listen in on the exchange of messagesbetween messaging stations 102 and 104 shown in FIG. 1 and performpassive positioning as described with respect to FIG. 1 through 6. Itshould be noted that FIG. 7 is meant only to provide a generalizedillustration of various components, any or all of which may be utilizedas appropriate.

The mobile device 700 is shown comprising hardware elements that can beelectrically coupled via a bus 705 (or may otherwise be incommunication, as appropriate). The hardware elements may include aprocessing unit(s) 710 which may comprise, without limitation, one ormore general-purpose processors, one or more special-purpose processors(such as digital signal processing (DSP) chips, graphics accelerationprocessors, application specific integrated circuits (ASICs), and/or thelike), and/or other processing structure or means, which can beconfigured to perform one or more of the methods described herein. Asshown in FIG. 7, some embodiments may have a separate DSP 720, dependingon desired functionality. The mobile device 700 also may comprise one ormore input devices 770, which may comprise without limitation one ormore touch screens, touch pads, microphones, buttons, dials, switches,and/or the like; and one or more output devices 715, which may comprisewithout limitation, one or more displays, light emitting diodes (LEDs),speakers, and/or the like.

The mobile device 700 might also include a wireless communicationinterface 730, which may comprise without limitation a modem, a networkcard, an infrared communication device, a wireless communication device,and/or a chipset (such as a Bluetooth device, an IEEE 802.11 device, anIEEE 802.15.4 device, a Wi-Fi device, a WiMAX device, cellularcommunication facilities, etc.), and/or the like. The wirelesscommunication interface 730 may permit data to be communicated with anetwork, wireless access points, other computer systems.

For example, in the context of wireless local area network (WLAN) datacommunications, wireless communication interface 730 may supportcommunication between the mobile device 700 and one or more accesspoints (APs). In the context of passive positioning, wirelesscommunication interface 730 may be used by mobile device 700 to capturepacketized messages exchanged between the messaging stations 102 and 104shown in FIG. 1. The communication can be carried out via one or morewireless communication antenna(s) 732 that send and/or receive wirelesssignals 734.

Depending on desired functionality, the wireless communication interface730 may comprise separate transceivers to communicate with basetransceiver stations and other wireless devices and access points. Thecommunication may be take place over different network types, includingbut not limited to a WLAN, wireless wide area network (WWAN), etc. Suchnetworks may be a Code Division Multiple Access (CDMA) network, a TimeDivision Multiple Access (TDMA) network, a Frequency Division MultipleAccess (FDMA) network, an Orthogonal Frequency Division Multiple Access(OFDMA) network, a Single-Carrier Frequency Division Multiple Access(SC-FDMA) network, a WiMax (IEEE 1002.16), and so on. A CDMA network mayimplement one or more radio access technologies (RATs) such as cdma2000,Wideband-CDMA (W-CDMA), and so on. Cdma2000 includes IS-95, IS-2000,and/or IS-856 standards. A TDMA network may implement Global System forMobile Communications (GSM), Digital Advanced Mobile Phone System(D-AMPS), or some other RAT. An OFDMA network may employ LTE, LTEAdvanced, and so on. LTE, LTE Advanced, GSM, and W-CDMA are described indocuments from 3GPP. Cdma2000 is described in documents from aconsortium named “3rd Generation Partnership Project 2” (3GPP2). 3GPPand 3GPP2 documents are publicly available. A WLAN may also be an IEEE802.11x network, and a WPAN may be a Bluetooth network, an IEEE 802.15x,or some other type of network. The techniques described herein may alsobe used for any combination of WWAN, WLAN, and/or WPAN.

The mobile device 700 can further include sensor(s) 740. Such sensorsmay comprise, without limitation, one or more accelerometer(s),gyroscope(s), camera(s), magnetometer(s), altimeter(s), microphone(s),proximity sensor(s), light sensor(s), and the like. Some or all of thesensor(s) 740 can be utilized, among other things, for dead reckoningand/or other positioning methods. Such positioning methods may be usedto independently or in combination with other devices and operations,including passive positioning as described herein, to determine orupdate a position of the mobile device 700.

Embodiments of the mobile device 700 may also include an SPS receiver780 capable of receiving signals 784 from one or more SPS satellitesusing an SPS antenna 782. Such positioning can be utilized to complementand/or incorporate the techniques described herein. The SPS receiver 780can extract a position of the mobile device, using conventionaltechniques, from SPS space vehicles (SVs) of an SPS system, such as GNSS(e.g., Global Positioning System (GPS)), Galileo, GLONASS, Compass,Quasi-Zenith Satellite System (QZSS) over Japan, Indian RegionalNavigational Satellite System (IRNSS) over India, Beidou over China,and/or the like. Moreover, the SPS receiver 780 can be used with variousaugmentation systems (e.g., a Satellite Based Augmentation System(SBAS)) that may be associated with or otherwise enabled for use withone or more global and/or regional navigation satellite systems. By wayof example but not limitation, an SBAS may include an augmentationsystem(s) that provides integrity information, differential corrections,etc., such as, e.g., Wide Area Augmentation System (WAAS), EuropeanGeostationary Navigation Overlay Service (EGNOS), Multi-functionalSatellite Augmentation System (MSAS), GPS Aided Geo Augmented Navigationor GPS and Geo Augmented Navigation system (GAGAN), and/or the like.Thus, as used herein an SPS may include any combination of one or moreglobal and/or regional navigation satellite systems and/or augmentationsystems, and SPS signals may include SPS, SPS-like, and/or other signalsassociated with such one or more SPS.

The mobile device 700 may further include and/or be in communicationwith a memory 760. The memory 760 may comprise, without limitation,local and/or network accessible storage, a disk drive, a drive array, anoptical storage device, a solid-state storage device, such as a randomaccess memory (“RAM”), and/or a read-only memory (“ROM”), which can beprogrammable, flash-updateable, and/or the like. Such storage devicesmay be configured to implement any appropriate data stores, includingwithout limitation, various file systems, database structures, and/orthe like.

The memory 760 of the mobile device 105 also can comprise softwareelements (not shown), including an operating system, device drivers,executable libraries, and/or other code, such as one or more applicationprograms, which may comprise computer programs provided by variousembodiments, and/or may be designed to implement methods, and/orconfigure systems, provided by other embodiments, as described herein.Merely by way of example, one or more procedures described with respectto the functionality discussed above might be implemented as code and/orinstructions executable by the mobile device 700 (and/or a processingunit within the mobile device 700, and/or another device of apositioning system). In an aspect, then, such code and/or instructionscan be used to configure and/or adapt a general-purpose computer (orother device) to perform one or more operations in accordance with thedescribed methods.

FIG. 8 illustrates an embodiment of the messaging stations 102 and 104,as an access point (AP) 800, which can be utilized as described hereinabove. As described previously, the messaging stations 102 and 104 areinvolved in the exchange of messages, which are captured by theobserving device 106, to perform passive positioning as described withrespect to FIG. 1 through 6. FIG. 8 is meant only to provide ageneralized illustration of various components, any or all of which maybe utilized as appropriate.

The access point 800 is shown comprising hardware elements that can beelectrically coupled via a bus 805 (or may otherwise be incommunication, as appropriate). The hardware elements may include aprocessing unit(s) 810 which may comprise, without limitation, one ormore general-purpose processors, one or more special-purpose processors(such as digital signal processing (DSP) chips, graphics accelerationprocessors, application specific integrated circuits (ASICs), and/or thelike), and/or other processing structure or means, which can beconfigured to perform one or more of the methods described herein. Asshown in FIG. 8, some embodiments may have a separate DSP 820, dependingon desired functionality. The access point 800 also may comprise one ormore output devices 815, which may comprise without limitation, one ormore displays, light emitting diodes (LEDs), speakers, and/or the like.

The access point 800 might also include a wireless communicationinterface 830, which may comprise without limitation a modem, a networkcard, an infrared communication device, a wireless communication device,and/or a chipset (such as a Bluetooth device, an IEEE 802.11 device, anIEEE 802.15.4 device, a Wi-Fi device, a WiMAX device, cellularcommunication facilities, etc.), and/or the like. The wirelesscommunication interface 830 may permit data to be communicated with anetwork, wireless access points, other computer systems.

For example, in the context of wireless local area network (WLAN) datacommunications, wireless communication interface 830 may supportcommunication between the access point 800 and one or more clientdevices, such as mobile device 700. In the context of passivepositioning, wireless communication interface 830 may be used by accesspoint 800 to exchange messages with other access points, as demonstratedby the exchange of messages between the messaging stations 102 and 104shown in FIG. 1. The communication can be carried out via one or morewireless communication antenna(s) 832 that send and/or receive wirelesssignals 834.

Depending on desired functionality, the wireless communication interface830 may comprise separate transceivers to communicate with clientdevices and other access points. The communication may take place overdifferent network types, including but not limited to a WLAN, wirelesswide area network (WWAN), etc. Such networks may be a Code DivisionMultiple Access (CDMA) network, a Time Division Multiple Access (TDMA)network, a Frequency Division Multiple Access (FDMA) network, anOrthogonal Frequency Division Multiple Access (OFDMA) network, aSingle-Carrier Frequency Division Multiple Access (SC-FDMA) network, aWiMax (IEEE 1002.16), and so on. A CDMA network may implement one ormore radio access technologies (RATs) such as cdma2000, Wideband-CDMA(W-CDMA), and so on. Cdma2000 includes IS-95, IS-2000, and/or IS-856standards. A TDMA network may implement Global System for MobileCommunications (GSM), Digital Advanced Mobile Phone System (D-AMPS), orsome other RAT. An OFDMA network may employ LTE, LTE Advanced, and soon. LTE, LTE Advanced, GSM, and W-CDMA are described in documents from3GPP. Cdma2000 is described in documents from a consortium named “3rdGeneration Partnership Project 2” (3GPP2). 3GPP and 3GPP2 documents arepublicly available. A WLAN may also be an IEEE 802.11x network, and aWPAN may be a Bluetooth network, an IEEE 802.15x, or some other type ofnetwork. The techniques described herein may also be used for anycombination of WWAN, WLAN, and/or WPAN.

Embodiments of the access point 800 may also include a wiredcommunication interface, such as a network interface card (NIC) 840, forconnecting to a larger network, e.g., the Internet, and/or a backhaul.In an upstream direction, access point 800 may use a wired communicationinterface such as NIC 840 to forward packetized messages received fromclient devices, such as mobile device 700, to the larger network and/orbackhaul. Similarly, in a downstream direction, access point 800 may usethe wired communication interface to forward packetized messagesreceived from the larger network and/or backhaul to client devices, suchas mobile device 700.

The access point 800 may further include and/or be in communication witha memory 860. The memory 860 may comprise, without limitation, localand/or network accessible storage, a disk drive, a drive array, anoptical storage device, a solid-state storage device, such as a randomaccess memory (“RAM”), and/or a read-only memory (“ROM”), which can beprogrammable, flash-updateable, and/or the like. Such storage devicesmay be configured to implement any appropriate data stores, includingwithout limitation, various file systems, database structures, and/orthe like.

The memory 860 of the access point 800 also can comprise softwareelements (not shown), including an operating system, device drivers,executable libraries, and/or other code, such as one or more applicationprograms, which may comprise computer programs provided by variousembodiments, and/or may be designed to implement methods, and/orconfigure systems, provided by other embodiments, as described herein.Merely by way of example, one or more procedures described with respectto the functionality discussed above might be implemented as code and/orinstructions executable by the access point 800 (and/or a processingunit within the access point 800, and/or another device of a positioningsystem). In an aspect, then, such code and/or instructions can be usedto configure and/or adapt a general-purpose computer (or other device)to perform one or more operations in accordance with the describedmethods.

It will be apparent to those skilled in the art that substantialvariations may be made in accordance with specific requirements. Withreference to the appended figures, components that may comprise memorymay comprise non-transitory machine-readable media. The terms“machine-readable medium” and “computer-readable medium” as used hereinrefer to any storage medium that participates in providing data thatcauses a machine to operate in a specific fashion. In embodimentsprovided hereinabove, various machine-readable media might be involvedin providing instructions/code to processing units and/or otherdevice(s) for execution. Additionally or alternatively, themachine-readable media might be used to store and/or carry suchinstructions/code. In many implementations, a computer-readable mediumis a physical and/or tangible storage medium. Such a medium may takemany forms, including but not limited to, non-volatile media, volatilemedia, and transmission media. Common forms of computer-readable mediainclude, for example, magnetic and/or optical media, punch cards, papertape, any other physical medium with patterns of holes, a RAM, a PROM,EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier waveas described hereinafter, or any other medium from which a computer canread instructions and/or code.

The methods, systems, and devices discussed herein are examples. Variousembodiments may omit, substitute, or add various procedures orcomponents as appropriate. For instance, features described with respectto certain embodiments may be combined in various other embodiments.Different aspects and elements of the embodiments may be combined in asimilar manner. The various components of the figures provided hereincan be embodied in hardware and/or software. Also, technology evolvesand, thus, many of the elements are examples that do not limit the scopeof the disclosure to those specific examples.

It has proven convenient at times, principally for reasons of commonusage, to refer to such signals as bits, information, values, elements,symbols, characters, variables, terms, numbers, numerals, or the like.It should be understood, however, that all of these or similar terms areto be associated with appropriate physical quantities and are merelyconvenient labels. Unless specifically stated otherwise, as is apparentfrom the discussion above, it is appreciated that throughout thisSpecification discussions utilizing terms such as “processing,”“computing,” “calculating,” “determining,” “ascertaining,”“identifying,” “associating,” “measuring,” “performing,” or the likerefer to actions or processes of a specific apparatus, such as a specialpurpose computer or a similar special purpose electronic computingdevice. In the context of this Specification, therefore, a specialpurpose computer or a similar special purpose electronic computingdevice is capable of manipulating or transforming signals, typicallyrepresented as physical electronic, electrical, or magnetic quantitieswithin memories, registers, or other information storage devices,transmission devices, or display devices of the special purpose computeror similar special purpose electronic computing device.

Terms, “and” and “or” as used herein, may include a variety of meaningsthat also is expected to depend at least in part upon the context inwhich such terms are used. Typically, “or” if used to associate a list,such as A, B, or C, is intended to mean A, B, and C, here used in theinclusive sense, as well as A, B, or C, here used in the exclusivesense. In addition, the term “one or more” as used herein may be used todescribe any feature, structure, or characteristic in the singular ormay be used to describe some combination of features, structures, orcharacteristics. However, it should be noted that this is merely anillustrative example and claimed subject matter is not limited to thisexample. Furthermore, the term “at least one of” if used to associate alist, such as A, B, or C, can be interpreted to mean any combination ofA, B, and/or C, such as A, AB, AA, AAB, AABBCCC, etc.

Having described several embodiments, various modifications, alternativeconstructions, and equivalents may be used without departing from thespirit of the disclosure. For example, the above elements may merely bea component of a larger system, wherein other rules may take precedenceover or otherwise modify the application of the invention. Also, anumber of steps may be undertaken before, during, or after the aboveelements are considered. Accordingly, the above description does notlimit the scope of the disclosure.

1. A method for estimating a position of an observing station,comprising: at the observing station, capturing a plurality ofpacketized Fine Timing Measurement (FTM) messages exchanged between apair of messaging stations comprising a first messaging station and asecond messaging station, the plurality of packetized FTM messagesincluding a first FTM message originating from the first messagingstation and intended for the second messaging station and furtherincluding a second FTM message originating from the second messagingstation and intended for the first messaging station; at the observingstation, determining a first time of arrival corresponding to a time atwhich the first FTM message arrives at the observing station, whereinthe first FTM message is part of an FTM session configured for animmediate, single burst by setting an As Soon As Possible (ASAP)parameter to a value of 1 and a burst exponent parameter to a value of0: (ASAP=1, burst exponent=0); at the observing station, determining asecond time of arrival corresponding to a time at which the second FTMmessage arrives at the observing station; obtaining, based on contentsof one of the plurality of packetized FTM messages, a firsttransmission-related time associated with transmission or reception ofthe first FTM message from the first messaging station to the secondmessaging station; obtaining, based on contents of one of the pluralityof packetized FTM messages, a second transmission-related timeassociated with transmission or reception of the second FTM message fromthe second messaging station to the first messaging station; andestimating the position of the observing station based on (1) a positionof the first messaging station, (2) a position of the second messagingstation, (3) the first time of arrival, (4) the second time of arrival,(5) the first transmission-related time, and (6) the secondtransmission-related time.
 2. The method of claim 1, wherein the firstFTM message is an FTM frame, and the second FTM message is anacknowledgement message acknowledging the FTM frame.
 3. The method ofclaim 2, wherein the first transmission-related time is a time ofdeparture (ToD) corresponding to transmission of the first FTM message,as a first FTM frame, M, from the first messaging station, and whereinthe second transmission-related time is a time of arrival (ToA)corresponding to reception of the second FTM message, as anacknowledgement frame for the first FTM frame, M, at the first messagingstation.
 4. The method of claim 3, wherein the firsttransmission-related time and second transmission-related time areobtained based on contents of a subsequent FTM frame, M+1.
 5. The methodof claim 1, wherein the configuration of the FTM session as animmediate, single-burst FTM session (ASAP=1, burst exponent=0) isrequested by one of the first and second messaging stations and notsubject to override by the other of the first and second messagingstations.
 6. The method of claim 1, wherein the FTM session is initiatedby an FTM request message, and the configuration of the FTM session asan immediate, single-burst FTM session (ASAP=1, burst exponent=0) isindicated by a bit in a trigger field in the FTM request message.
 7. Themethod of claim 1, wherein at least one of the captured packetized FTMmessages utilizes a modified FTM frame format, wherein the modified FTMframe format replaces a plurality of information element (IE) parameterfields with a plurality of new fields, and wherein the plurality of newfields includes one or more of a Max Burst Duration field, a Min DeltaFTM field, a Max FTMs per burst field, a FTM Format and Bandwidth field,a Status field, or a reserved field.
 8. The method of claim 1, whereinestimating the position of the observing station comprises: determininga differential distance corresponding to a difference between (a) adistance between the first messaging station and the observing stationand (b) a distance between the second messaging station and theobserving station; wherein the differential distance is determined basedon (1) the first time of arrival, (2) the second time of arrival, (3)the first transmission-related time, and (4) the secondtransmission-related time; and determining the position of the observingstation based on the differential distance, the position of the firstmessaging station, and the position of the second messaging station. 9.The method of claim 1, further comprising: obtaining the position of thefirst messaging station and the position of the second messaging bydownloading, from a server, a portion of an almanac comprising a list ofmessaging stations and corresponding locations.
 10. The method of claim1, further comprising: capturing a plurality of packetized FTM messagesexchanged between a second pair of messaging stations; whereinestimating the position of the observing station is further based onpositions of the second pair of messaging stations, times of arrival, atthe observing station, of a first and a second FTM message associatedwith the second pair of messaging stations, and first and secondtransmission-related times corresponding to the first and second FTMmessages associated with the second pair of messaging stations.
 11. Anapparatus for estimating a position of an observing station, comprising:a wireless communication interface configured to capture a plurality ofpacketized Fine Timing Measurement (FTM) messages exchanged between apair of messaging stations comprising a first messaging station and asecond messaging station, the plurality of packetized FTM messagesincluding a first FTM message originating from the first messagingstation and intended for the second messaging station and furtherincluding a second FTM message originating from the second messagingstation and intended for the first messaging station; a processing unitcoupled to the wireless communication interface, the processing unitconfigured to determine, at the observing station, a first time ofarrival corresponding to a time at which the first FTM message arrivesat the observing station, wherein the first FTM message is part of anFTM session configured for an immediate, single burst by setting an AsSoon As Possible (ASAP) parameter to a value of 1 and a burst exponentparameter to value of 0: (ASAP=1, burst exponent=0); wherein theprocessing unit is further configured to determine, at the observingstation, a second time of arrival corresponding to a time at which thesecond FTM message arrives at the observing station; wherein theprocessing unit is further configured to obtain, based on contents ofone of the plurality of packetized FTM messages, a firsttransmission-related time associated with transmission or reception ofthe first FTM message from the first messaging station to the secondmessaging station; wherein the processing unit is further configured toobtain, based on contents of one of the plurality of packetized FTMmessages, a second transmission-related time associated withtransmission or reception of the second FTM message from the secondmessaging station to the first messaging station; and wherein theprocessing unit is further configured to estimate the position of theobserving station based on (1) a position of the first messagingstation, (2) a position of the second messaging station, (3) the firsttime of arrival, (4) the second time of arrival, (5) the firsttransmission-related time, and (6) the second transmission-related time.12. The apparatus of claim 11, wherein the first FTM message is an FTMframe, and the second FTM message is an acknowledgement messageacknowledging the FTM frame.
 13. The apparatus of claim 12, wherein thefirst transmission-related time is a time of departure (ToD)corresponding to transmission of the first FTM message, as a first FTMframe, M, from the first messaging station, and wherein the secondtransmission-related time is a time of arrival (ToA) corresponding toreception of the second FTM message, as an acknowledgement frame for thefirst FTM frame, M, at the first messaging station.
 14. The apparatus ofclaim 13, wherein the first transmission-related time and secondtransmission-related time are obtained based on contents of a subsequentFTM frame, M+1.
 15. The apparatus of claim 11, wherein the configurationof the FTM session as an immediate, single-burst FTM session (ASAP=1,burst exponent=0) is requested by one of the first and second messagingstations and not subject to override by the other of the first andsecond messaging stations.
 16. The apparatus of claim 11, wherein theFTM session is initiated by an FTM request message, and theconfiguration of the FTM session as an immediate, single-burst FTMsession (ASAP=1, burst exponent=0) is indicated by a bit in a triggerfield in the FTM request message.
 17. The apparatus of claim 11, whereinat least one of the captured packetized FTM messages utilizes a modifiedFTM frame format, wherein the modified FTM frame format replaces aplurality of information element (IE) parameter fields with a pluralityof new fields, and wherein the plurality of new fields includes one ormore of a Max Burst Duration field, a Min Delta FTM field, a Max FTMsper burst field, a FTM Format and Bandwidth field, a Status field, or areserved field.
 18. The apparatus of claim 11, wherein the processingunit is configured, as part of estimating the position of the observingstation, to: determine a differential distance corresponding to adifference between (a) a distance between the first messaging stationand the observing station and (b) a distance between the secondmessaging station and the observing station; wherein the differentialdistance is determined based on (1) the first time of arrival, (2) thesecond time of arrival, (3) the first transmission-related time, and (4)the second transmission-related time; and determining the position ofthe observing station based on the differential distance, the positionof the first messaging station, and the position of the second messagingstation.
 19. The apparatus of claim 11, wherein the processing unit isfurther configured to: obtain the position of the first messagingstation and the position of the second messaging by downloading, from aserver, a portion of an almanac comprising a list of messaging stationsand corresponding locations.
 20. The apparatus of claim 11, wherein thewireless communication interface is further configured to capture aplurality of packetized FTM messages exchanged between a second pair ofmessaging stations; and wherein the processing unit is configured toestimate the position of the observing station, further based onpositions of the second pair of messaging stations, times of arrival, atthe observing station, of a first and a second FTM message associatedwith the second pair of messaging stations, and first and secondtransmission-related times corresponding to the first and second FTMmessages associated with the second pair of messaging stations.
 21. Asystem for estimating a position of an observing station, comprising:means for, at the observing station, capturing a plurality of packetizedFine Timing Measurement (FTM messages exchanged between a pair ofmessaging stations comprising a first messaging station and a secondmessaging station, the plurality of packetized FTM messages including afirst FTM message originating from the first messaging station andintended for the second messaging station and further including a secondFTM message originating from the second messaging station and intendedfor the first messaging station; means for, at the observing station,determining a first time of arrival corresponding to a time at which thefirst FTM message arrives at the observing station, wherein the firstFTM message is part of an FTM session configured for an immediate,single burst by setting an As Soon As Possible (ASAP) parameter to avalue of 1 and a burst exponent parameter to value of 0: (ASAP=1, burstexponent=0); means for, at the observing station, determining a secondtime of arrival corresponding to a time at which the second FTM messagearrives at the observing station; means for obtaining, based on contentsof one of the plurality of packetized FTM messages, a firsttransmission-related time associated with transmission or reception ofthe first FTM message from the first messaging station to the secondmessaging station; means for obtaining, based on contents of one of theplurality of packetized FTM messages, a second transmission-related timeassociated with transmission or reception of the second FTM message fromthe second messaging station to the first messaging station; and meansfor estimating the position of the observing station based on (1) aposition of the first messaging station, (2) a position of the secondmessaging station, (3) the first time of arrival, (4) the second time ofarrival, (5) the first transmission-related time, and (6) the secondtransmission-related time.
 22. The system of claim 21, wherein the firstFTM message is an FTM frame, and the second FTM message is anacknowledgement message acknowledging the FTM frame.
 23. The system ofclaim 22, wherein the first transmission-related time is a time ofdeparture (ToD) corresponding to transmission of the first FTM message,as a first FTM frame, M, from the first messaging station, and whereinthe second transmission-related time is a time of arrival (ToA)corresponding to reception of the second FTM message, as anacknowledgement frame for the first FTM frame, M, at the first messagingstation.
 24. The system of claim 23, wherein the firsttransmission-related time and second transmission-related time areobtained based on contents of a subsequent FTM frame, M+1.
 25. Thesystem of claim 21, wherein the configuration of the FTM session as animmediate, single-burst FTM session (ASAP=1, burst exponent=0) isrequested by one of the first and second messaging stations and notsubject to override by the other of the first and second messagingstations.
 26. The system of claim 21, wherein the FTM session isinitiated by an FTM request message, and the configuration of the FTMsession as an immediate, single-burst FTM session (ASAP=1, burstexponent=0) is indicated by a bit in a trigger field in the FTM requestmessage.
 27. A non-transitory computer-readable storage mediumcomprising machine-readable instructions stored thereon, theinstructions, when executed by one or more processors, causing the oneor more processors to: at an observing station, facilitate capturing aplurality of packetized Fine Timing Measurement (FTM) messages exchangedbetween a pair of messaging stations comprising a first messagingstation and a second messaging station, the plurality of packetized FTMmessages including a first FTM message originating from the firstmessaging station and intended for the second messaging station andfurther including a second FTM message originating from the secondmessaging station and intended for the first messaging station; at theobserving station, determine a first time of arrival corresponding to atime at which the first FTM message arrives at the observing station,wherein the first FTM message is part of an FTM session configured foran immediate, single burst by setting an As Soon As Possible (ASAP)parameter to a value of 1 and a burst exponent parameter to value of 0:(ASAP=1, burst exponent=0); at the observing station, determine a secondtime of arrival corresponding to a time at which the second FTM messagearrives at the observing station; obtain, based on contents of one ofthe plurality of packetized FTM messages, a first transmission-relatedtime associated with transmission or reception of the first FTM messagefrom the first messaging station to the second messaging station;obtain, based on contents of one of the plurality of packetized FTMmessages, a second transmission-related time associated withtransmission or reception of the second FTM message from the secondmessaging station to the first messaging station; and estimate theposition of the observing station based on (1) a position of the firstmessaging station, (2) a position of the second messaging station, (3)the first time of arrival, (4) the second time of arrival, (5) the firsttransmission-related time, and (6) the second transmission-related time.